For you reading pleasure, the dissertation "Investigation of Through-Tenon Keys on the Tensile Strength of Mortise and Tenon Joints" by Lance David Shields http://scholar.lib.vt.edu/theses/available/etd-07112011-100606/unrestricted/Shields_LD_T_2011.pdfJim
The closer you look the more you see.
"Heavy timber framing is not a lost art" Fred Hodgson, 1909
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